Whether the growing attention to concussions in young athletes will lead to an exodus from the football field (or the basketball court, or the hockey rink) will say a lot about how we humans process risk. Which means it’s anybody’s guess.

If history is any guide, we seem to veer between overreaction and underreaction — all while defining our own response as “moderate.” There is an inherent hypocrisy in our attempts to control our odds — putting the organic veggies (there is no actual data proving that organic foods increase longevity) in the trunk of our car (researchers tell us there is “evidence” but not “proof” that car emissions accelerate heart disease), then checking our e-mail on our cellphone at the next red light (2,600 traffic deaths a year are caused by drivers using cellphones, according to a Harvard study).

And while we certainly make constant (mis)calculations in our adult lives, we seem all the more determined yet befuddled when it comes to the safety of our children. For instance, the five things most likely to cause injury to children up to age 18, according to the Centers for Disease Control and Prevention, are: car accidents, homicide (usually at the hands of someone they know), child abuse, suicide or drowning. And what are the five things that parents are most worried about (according to surveys by the Mayo Clinic)? Kidnapping, school snipers, terrorists, dangerous strangers and drugs.

“Parents are just bad at risk assessment,” said Christie Barnes, a mother of four and the author of “The Paranoid Parents Guide.” “We are constantly overestimating rare dangers while underestimating common ones.”

We probably do this because our brains are not designed to process abstract or long-term risk. We were built to hear a sound, determine whether it is the growl of a saber-tooth, and then decide to run or go back to sleep. But in a world where you can hear the roar of what may or may not be a tiger (or a kidnapped child) in Montana while you are sitting in your kitchen in Florida, it’s tough to assess personal danger. With worst-case scenarios being thrown our way hourly on TV and the Internet, our sense of proportion and ratio becomes muddled.

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Tim Bower

“The least safe thing you can do with your child, statistically, is drive them somewhere,” said Lenore Skenazy, author of “Free-Range Kids,” a manifesto preaching a return to the day when children were allowed to roam on their own. “Yet every time we put them in the car we don’t think, ‘Oh God, maybe I should take public transportation instead, because if something happened to my kid on the way to the orthodontist I could never forgive myself.’ ”

So we put them in that car and we drive — to the orthodontist, to school, to their friend’s house two blocks away — because “if I let them walk and they were abducted I would never forgive myself.” This despite the fact that the British writer Warwick Cairns, author of “How to Live Dangerously,” has calculated that if you wanted to guarantee that your child would be snatched off the street, he or she would have to stand outside alone for 750,000 hours. And while we are busy inflating some risks, we tend not to focus on others — like the obesity and diabetes that result when children are driven someplace when they could walk, or when they play video games inside instead of playing in the park.

Perversely, our worry seems to be increasing at a time when actual risk is decreasing. “Homicide is down, kidnapping is down, traffic deaths are down,” Ms. Barnes said. What is up, however, is measurement. It seems as if there’s a statistic for everything, and many of the numbers change from one study to the next. This means we are increasingly being asked to be expert in areas where even the experts aren’t certain.

The onslaught of numbers also leads us to whittle risk into tiny increments. “A kid growing up has to go through seven different changes of car seat by law in some states,” said Dr. Daniel Perl, a professor of pathology at Uniformed Services University of the Health Sciences in Bethesda, Md., the medical school for the United States military, “and what that prevents in terms of injuries or deaths are probably a couple of handfuls. Yet we have over four million kids playing football. Moms will take their 7-year-olds in the car, in a state-of-the-art car seat, to go and play football.”

Which brings us back to the beginning.

There is no question that children get hurt playing football. The sport accounts for 22 percent of all concussions among 8- to 19-year-olds; 27 percent of football players ages 12 through 17 have had a least one concussion. That will not be news to any mother who has squinted through her fingers as her son is tackled on a Saturday afternoon. What will be news, though, is last week’s link between teenage football and chronic traumatic encephalopathy, which is what Boston University researchers found in the brain of Owen Thomas, 21, the Penn student who killed himself in April.

So far, there is only one case. Still, what is a parent to do? “Some people may look at this study and say, ‘That’s it, Johnny; you’re taking up chess,’ ” said Dr. Perl, who stressed that he was speaking as an experienced neuropathologist and not on behalf of the Department of Defense.

On the other hand, he notes, the existing data on athletes with C.T.E. consists of 51 autopsies, most of those on boxers, not football players. And there are benefits to football — the feeling of belonging to a team, the physical exercise, the potential college scholarship, perhaps the pride in carrying on a family tradition — that will outweigh the risks for some families, assuming those risks can ever actually be quantified.

“Right now I don’t know that it’s calculable, but it’s estimatable,” Dr. Perl said, adding that he wouldn’t venture to make an estimate. “And you can’t really make a recommendation based on one case. So it’s up to a young player’s parents to decide.”

A version of this article appears in print on September 19, 2010, on Page WK4 of the New York edition with the headline: To Keep a Child Safe, Just ... Order Reprints|Today's Paper|Subscribe